The present invention relates to methods of separating oil from oil-containing seeds, involving aerating an aqueous dispersion of germ particles of oil-containing seeds (e.g., corn) to produce bubbles therein, whereby the oil in the aqueous dispersion adheres preferentially to the surfaces of the bubbles and are carried by the bubbles to the upper surface of the aqueous dispersion where a foam of the bubbles is formed; separating the foam from the aqueous dispersion; and recovering the oil from the foam. The aqueous dispersion of germ particles of oil-containing seeds may be produced by mixing corn germ separated from corn kernels with an aqueous acetate buffer followed by heating, grinding, cooling, and optionally agitation; generally cellulase is added after the grinding.
Corn oil is currently extracted from the germ products of dry- and wet-milled corn by hexane extraction or by pressing with specially designed screws (expellers). The plants which use these methods were built to produce higher value products (e.g., food and starch) in comparison to plants making ethanol, and the germ separation and oil extraction (which sometimes occurs in a separate plant) is secondary to large grit (dry-mill) or clean starch (wet-mill) products. As a result of the recent construction of a large number of dry grind (DG) ethanol plants there is a significant amount of corn oil in corn germ available for separation from the ethanol-coproduct called distillers dry grains. About 3.5 million liters of corn oil can be obtained annually from a typical DG plant by centrifuging the concentrated stillage, although centrifugation is energy intensive. More and higher quality oil can be separated from the corn prior to fermentation to make fuel ethanol; however, the front end separation capital cost is as much as ten times higher than separation after fermentation (McElroy, A., Corn oil extraction opens new markets, Distillers Grains Quarterly, 1st Quarter 2007), mainly because front end corn fractionation requires the germ to be separated from the rest of the kernel which is not usually done. Thus currently used oil separation methods have sufficiently high capital costs to discourage retrofitting DG plants for front end germ separation and oil extraction. New germ separation methods have been developed to a pilot scale (Singh, V., and S. Eckhoff, S., Cereal Chem., 74(4): 462-466 (1997); Johnston, D., et al., J. Am. Oil Chem. Soc., 82(8): 603-608 (2005)) but there remains a need for a low cost process to recover oil from germ.